1. Technical Field
The invention relates to a zoom lens suitable for a television camera, a video camera or the like, and more particularly to a zoom lens having a focusing group closer to the object side than a variator group and adapted to focus by moving some of its lens groups, as well as an image pickup apparatus having the zoom lens.
2. Description of the Related Art
As a large-aperture, high zoom-ratio zoom lens suitable for a television camera or a video camera, a four-group type zoom lens has been known which includes, in order from the object side, a focusing group having a positive refractive power, a variator group having a negative refractive power, a compensation group having a positive or negative refractive power, and a relay lens group having a positive refractive power. In addition, among such four-group type zoom lenses, an inner focus type lens has been known in which the focusing group is divided into a plurality of lens groups, and focusing is effected by moving some of its divided lens groups. For example, Japanese Patent No.3495772 (corresponding to U.S. Pat. No. 5,760,967) discloses a four-group inner focus type zoom lens in which a focusing group is divided, in order from the object side, into three lens groups, i.e., a group A having a negative refractive power, a group B1 having a positive refractive power, and a group B2 having a positive refractive power. Of these groups, the group B1 and the group B2 are moved. In the zoom lens disclosed in Japanese Patent No.3495772, when the zoom lens focuses from an infinitely distant object to a close-range object, focusing is effected so that the group B1 and the group B2 are moved to the object side with different amounts of movement, and that if the condition of MB2/MB1<1 is satisfied where MB1 and MB2 denote the amounts of movement of the group B1 and the group B2, respectively.
However, as for the zoom lens disclosed in Japanese Patent No.3495772, in the focusing group which, as a whole, has a positive refractive power, the first group (the group A) is constructed with the negative refractive power. Therefore, the positive refractive power of the second group (the group B1) and the third group (the group B2) must be made large. As a result, the thicknesses of the second group and the third group and the lens diameter tend to become large, and the mass tends to increase, so that there arises a problem that operability during focusing becomes poor.